The Paris Agreement rallied more than 190 countries under the common goal of keeping a global temperature rise this century well below 2°C above pre-industrial levels. In the most optimistic scenario, the agreement would have countries limit warming to 1.5°C — this seemingly negligible 0.5°C would make a huge difference worldwide, ensuring that the planet suffers fewer and less intense droughts, floods, heatwaves, and poverty for millions of people. This target would also save countless species of wildlife.

Although highly ambitious, going even beneath the 1.5°C of warming is theoretically achievable — but only if action is immediately taken to phase out fossil fuels as soon as possible. According to a recent study, there’s a 66% chance of achieving this goal if the world’s fossil fuel infrastructure was phaseout at the end of its lifetime and no new infrastructure is added — all in the next four decades.

Researchers at the University of Leeds used various computer models to assess global temperature rise if the world was serious about ditching fossil fuels for good. The researchers considered a lifespan of 40 years for power plants, 15 years for vehicles, and 26 years for aircraft. The study also assumed that beef (which releases ten times more greenhouse gases than chicken) and dairy consumption will lower to minimal levels.

In other words, this is a very extremely ambitious scenario — and to be cynical, it’s also unrealistic. It implies that all the vehicles in the world will be electric (and with energy sourced from renewables) only 15 years from now. Given the pace of population growth but also purchasing power in developing countries, it would be an achievement if greenhouse emissions from the livestock sector plateau rather than face a steep decline. And according to Carbon Brief, 200 gigawatts (GW) of coal-fired power plants are currently being built and 450GW of capacity is planned — these would all have to be canceled and not allowed burn a single lump of coal. Let’s not mention the fact that there is no current alternative to fossil fuel-powered airplanes, although some manufacturers are researching an electric alternative.

Even so, if phaseout does not begin by 2030, the researchers estimate there’s a 33% chance of limiting warming to 1.5°C. That’s better than nothing. What’s more, it’s important to set big goals so that our efforts might be stretched to their limit.

“We are going the right way, but I don’t think we will do enough, quickly enough. I think we are heading for 2C to 2.5C,” Christopher Smith, of the University of Leeds, who led the research, told The Guardian.

But he added: “If you don’t have a goal, you are not going to get anywhere. If you have a target that is really hard to achieve and you miss it slightly, that is better than wandering aimlessly into a future climate that is no good for anybody.”